Two-terminal resistance random access memory is actively being developed as large-capacity nonvolatile memory to replace conventional floating-gate type NAND flash memory. Low voltage/low current operations, high speed switching, and downscaling/higher integration of the memory cells are possible for this type of memory. Various materials are being proposed for the variable resistance layer of resistance random access memory, among which ionic memory is promising because ionic memory includes a silicon layer or a silicon oxide layer, which are compatible with existing LSI processes, as the variable resistance layer. Ionic memory includes silver (Ag) as the ion source electrode. Ionic memory has the advantages such as and low current operations, and rectifying operations. In ionic memory, the on/off operations of the memory cell are realized by causing a filament of silver to precipitate in and disappear from the variable resistance layer.
Generally, a trade-off relationship exists between the data retention characteristics and the ease of resetting data for nonvolatile memory. For ionic memory as well, in the case of a variable resistance layer configured to have good retention characteristics, the filament that is formed inside the variable resistance layer in the set state is stable; and therefore, a high voltage must be applied to perform the reset operation, that is, to cause the filament to disappear. The memory operations are harmed by applying the high voltage because the rewriting durability degrades.